In recent years, formation of finer patterns by lithography has been rapidly advanced in a manufacturing process of a semiconductor element, a liquid crystal element, and the like. As a method for forming a finer pattern, the wavelength of irradiating light is shortened.
Recently, a KrF excimer laser (wavelength: 248 nm) lithographic technique has been introduced, and an ArF excimer laser (wavelength: 193 nm) lithographic technique and an EUV (wavelength: 13.5 nm) lithographic technique have been investigated in order to further shorten the wavelength.
Acrylic copolymers that are transparent with respect to light having a wavelength of 193 nm have attracted attention as a copolymer for chemically amplified resist used in the ArF excimer laser lithography. For example, a copolymer for resist formed using a (meth)acrylic acid ester as a monomer is described in the following Patent Document 1.
However, it is general that a copolymer of a (meth)acrylic acid ester is polymerized by a radical polymerization method. Generally, in a copolymer of a multicomponent system composed of two or more kinds of monomers, the composition (copolymer composition) of the monomer units in the copolymer to be produced in an initial stage of polymerization differs from that in a later stage of polymerization since the copolymerization reactivity ratio among the respective monomers is different, and thus the copolymer to be obtained has a composition distribution.
There is a case in which the preparation of the resist composition is interfered as the solubility of the resist composition in a solvent is likely to be non-uniform so that the resist composition precipitates when being stored at a low temperature, it takes a long time to dissolve the resist composition in a solvent when being prepared, or the number of manufacturing processes increases due to the generation of insoluble matters when the composition of the monomer units in the copolymer varies. In addition, the sensitivity of the resist composition to be obtained is likely to be insufficient.
For example, a method for manufacturing a copolymer for photoresist is described in Patent Document 2 which includes a supply step of supplying a monomer solution and a solution containing a polymerization initiator to a polymerization reaction system in order to obtain a highly sensitive resist and in which the fluctuation of the composition of unreacted monomers present in the polymerization reaction system is small from the start of the polymerization reaction to the completion of supply of the monomer solution.
A method is described in Patent Document 3 in which a portion of the monomer having an acid leaving group among the monomers used in the manufacture of the copolymer for resist is supplied to a reaction vessel in advance and the rest of the monomer having an acid leaving group and a mixture of other monomers are added to the reaction vessel dropwise to polymerize them. In the dropping polymerization method, a copolymer having a higher molecular weight is produced in an initial stage of the polymerization reaction and a copolymer having a lower molecular weight is then produced as the polymerization reaction proceeds, and thus a copolymer in which an acid leaving group exhibiting low polarity is contained more on the higher molecular weight side to be produced in the initial stage of the polymerization is obtained by setting only the acid leaving group present in the reaction vessel in advance.